A polarizing plate that is applied to various types of image display devices such as liquid crystal display devices, plasma display devices, and electroluminescences has a structure that includes a polarizer formed of a polyvinyl alcohol-based film and a transparent protective film formed on at least one side of the polarizer. In connection with this, examples of an adhesive for a polarizing plate that is used to attach the polarizer and the transparent protective film to each other include a water-based adhesive. In particular, a polyvinyl alcohol-based adhesive in which a crosslinking agent is mixed with a polyvinyl alcohol aqueous solution is used.
Currently, the high-quality image display device is required. The high-quality image display device has a slim and light structure, uniformity, heat resistance, moisture resistance, and a waterproofing property, thereby ensuring high precision and high performance. Accordingly, it is required that the adhesive that is applied to the image display device has the moisture resistance and the waterproofing property and delaminating is prevented in a humid atmosphere.
To satisfy the requirement, JP-A-7-198945 discloses an adhesive for a polarizing plate that includes a polyvinyl alcohol-based resin with an acetoacetyl group and a crosslinking agent.
However, the adhesive for the polarizing plate is problematic in that a stain is generated in the alkali pH condition, storage stability (pot life) of the adhesive is short, the moisture resistance and the waterproofing property are poor, and yellowing occurs to change the color of the polarizing plate when a heat resistance evaluation is performed in the acidic pH condition.